by Alastair Denniston- Code-breaking From Room 40 to Berkeley Street
Ciez’ki proceeded to demonstrate, with the assistance of an Enigma machine which included a plugboard, how the Poles had gone about working out the daily setting of the machine. Once this was known, they could read the messages by simply typing the encrypted text into their Enigma machines. The British and the French attendees were then shown the Zygalski sheets, cyclometer and bombas. Knox, in his position as the British expert, stood close to the machines during the demonstration. During a break for tea after three hours, and then afterwards, AGD’s worst fears about Knox’s attendance at the meeting were realised. He maintained a stony silence throughout the meeting and was clearly upset by what he was hearing. Matters came to a head when they got into a car to leave, as AGD later recalled:
It was only when we got back in the car to drive away that he (Knox) suddenly let himself go and assuming that no one understood any English raged and raged that they were lying to us now as in Paris. The whole thing was a pinch he kept on repeating – they never worked it out – they pinched it years ago and have followed developments as anyone could but they must have bought it or pinched it.83
Knox probably knew more about the Enigma machine than anyone in Britain at the time of the Pyry meetings. While he had some success in breaking versions of the Enigma machine which were similar to the early commercial version, he had been unable to break the new military version with the plugboard. His problem had been the connections between the keyboard and the entry drum inside the machine. On the models of Enigma machines that he had successfully broken, the connection pattern followed the order of the keys left to right, row by row and alphabetically around the entry drum. So the Q key was connected to A, W key to B, E key to C, R key to D, etc. On the model of Enigma in mass use by the German Army and Air Force, the connection pattern had been changed and Knox’s team (which included Turing) could not work out the new pattern. This problem had also stumped Rejewski initially, and he described his solution in a paper written in 1980:
What, then, were the connections in the entry drum? It turned out later that they can be found by deduction, but in December 1932, or perhaps in the first days of 1933, I obtained those connections by guessing. I assumed that since the keyboard keys were not connected with the successive contacts in the entry drum in the order of the letters on the keyboard, then maybe they were connected up in alphabetical order; that is, that the permutation caused by the entry drum was an identity and need not be taken into account at all. This time luck smiled upon me. The hypothesis proved correct, and the very first trial yielded a positive result.84
When Knox met Rejewski he had quickly asked him: ‘What are the connections to the entry drum?’ Knox was furious when he heard the answer; ‘A, B, C, —-’. In other words, the Germans had wired it up in the simplest possible way, the Q key to Q, the W key to W, the E key to E, the R key to R, etc. He remained aloof and alone over dinner and gave the impression that he had a grudge against the Poles. AGD spoke with Bertrand and Sandwith and it was decided to return to Warsaw as soon as possible. The next day, Knox met with Langer, Ciez’ki, Rejewski, Zygalski and Różycki. According to AGD, Knox was ‘his own bright self & won the hearts & admiration of the young men with whom he was so much in touch’. Ever the loyal colleague, AGD explained Knox’s behaviour as follows: ‘If only that first day of formal disclosure could have been avoided & pompous declarations by senior officers had been omitted. Knox’s mind & personality in touch with men who really knew their job would have made that visit a very real success. They were all simple & straightforward.’
AGD and Sandwith left on the 28th to return to home and he was back in London by Sunday the 30th. The following day he wrote to Bertrand:
My dear Colonel,
Our party returned safely if with difficulty. Mr. Knox’s papers were not quite in order and he had to spend the night in Posen, but arrived safely 24 hours later.
I wish again to assure you our extreme gratitude for all that you did for us and our appreciation of your very fine achievements. I have reported the matter in brief to my Chief who also expressed freely his appreciation of your work as I described it. He empowers me to repeat our invitation for you and the Major to visit us.
I trust such a visit may be in the near future, but the next few weeks are unusual with us owing to manoeuvres, and I also think it might be a good thing to get our cooperation started on the lines we outlined before you came, in order that any weak points might be noted and eliminated.
In accordance with the desire of your staff I hope to send by an early courier our intercepts of the T.G.D. group and these I will continue to send by each courier via our mutual friend Captain B. I am also sending our interception of the Naval material during the month of May 1937, as our experts felt that the additional material at that period might prove of great value to them.
Mr. Knox is now organising his staff to continue investigations on the Military material on the lines suggested by your experts.
I shall be grateful, my dear Colonel, if you will convey to Colonel S. and Colonel M. our gratitude and in the hope that our close collaboration may achieve further useful results.85
AGD had agreed with the Poles that the British, with greater resources at their disposal, would produce the Zygalski sheets.86
Knox’s passport had been wrongly stamped for a return journey through Germany. Instead, he had to travel to Poznan to get a visa from the British Consul there. AGD’s patience with Knox must have been sorely tested when he received a letter from him, written on Hotel Bristol notepaper and dated 30 July:
My Dear Alastair
Let’s get this straight.
The Poles have got the machine to Sept 15th 38 out by luck. As I have said only Mrs B.B. had seriously contemplated the equation A = 1 B = 2. Had she worked on the crib we should be teaching them.
They must have done very well to determine the two new wheels. How they did it might be important. I have not discussed this.
Their machine for determining all ciphers (O.S.) and SSD (n.s.) may be good. If we are going to read them we should be given a detailed study: if not, we only want the broadest outline of its electrical principles.
Military (?) Sept 15 – ?? April 1 ??. Here they seem to have failed badly Mathematically the data are more not less than with the other cipher (if there be over 300 messages). If we are to attempt this we should examine their system and statistics (if any) with considerable scepticism*. Why have they failed on an astronomical but simple calculation.
April 1st (??) to now. The whole basis of diagnosis may have changed though doubtless the machine remains.
Before deciding anything we must settle
Whether we are going to give a miss to the S.S.D. stuff
Whether they have got the right system for the other.
I am fairly clear that Schessky [Knox is referring to Ciez’ki] knows very little about the machine & may try to conceal facts from us.
The young men seem very capable and honest.
A.D.K.
Finally (f) It cannot too strongly be emphasised that all successes have depended on a factor (the machine coding of indicators) which may at any moment be cancelled.
Even the principle of electrical selection must be viewed with distrust.87
It is typical of Knox that he ends his rant against the Poles with kind words for Rejewski, Zygalski and Różycki. He was also correct in pointing out the weakness in the Polish methods, i.e. their dependence on the machine coding of indicators. This was indeed cancelled in early May 1940, rendering the Polish methods useless.88
Despite being friends with Knox since their Room 40 days, AGD revealed his exasperation in a remarkably candid letter to Bertrand, dated 3 August 1939. It was written on the same Hotel Bristol note paper that Knox had used:
My dear Bertrand,
I have finally had a day off and I take this opportunity to write to you a very personal letter, ‘from the heart’, which seems necessary to me.
I have seen D;89 in h
is opinion I may have said something bad about you and that is why I wish to emphasise that we owe everything solely to you and I look forward to the cooperation of our trio and, that to reach our goal you must remain in the leading position. In Warsaw it was you who advised me to return and think about it – and you were right.
Maybe you understand my problem in the shape of Knox. He is a man of exceptional intelligence, but he does not know the word cooperation. You surely must have noticed that off duty, he is a pleasant chap loved by all. But in the office his behaviour is different.
In Warsaw I had some deplorable experiences with him. He wants to do everything himself. He does not know how to explain anything. He can’t stand it when someone knows more than him. Unfortunately, I cannot do without him, he knows more about the machine than anyone else in the country. He built a machine of the type used by the Spanish, and frequently by the Italians in Spain, which is not to be sneered at, even if not so much has been done as has been done by our friends in Z.
You must forgive me for being so keen to keep him, but I will tell you in all sincerity, that I will never take him to a conference again if I can only avoid it. From now on, we must establish the rules of our cooperation in order to avoid unnecessary effort.
The Pyry meeting came just in time because on 1 September, Germany invaded Poland and two days later, Britain declared war on Germany. By 10 September 1939, German forces were rolling relentlessly across Poland and their armoured columns broke through near Warsaw. The Polish Cipher Department was ordered to leave the capital and the Pyry Centre as soon as possible and move its essential equipment. However, the advance of the Red Army into Poland on 17 September made the Poles change their plans. The cryptanalysts were forced to destroy all traces of their equipment and documents, retaining several Enigmas. The military and civilian sections of the Cipher Department split after they crossed the border into Romania. On 20 September Bertrand delivered a replica Enigma to Menzies in London as a gift from the Poles. The Polish contribution to the early success of BP would prove to be significant. They had recognised in the late 1920s that the age of machine cryptography had begun and that mathematicians would be effective as cryptanalysts.
While it is likely that Knox came away from the Pyry conference with the missing link in his attempt to construct the Enigma machine itself, AGD clearly saw the bigger picture, and on returning to Britain began to recruit more mathematicians for GC&CS. The Poles had demonstrated to the British that encryption machines like Enigma could be broken, if the right mathematical minds were allowed to concentrate on the problem. With the prospect of many years of war ahead, AGD’s knowledge and experience of Sigint and its effectiveness in military conflict, would certainly be put to the test.
Chapter 4
Bletchley Park
AGD and his family had moved to Ashtead in Surrey in 1937. They enjoyed their tall, thin house at 48 Tedworth Square, Chelsea, and AGD had a twenty-year lease on the property. They also had a bungalow, called Greengates, in Fairfield Road, Barton-on-Sea, Hampshire, where they spent the summers. They went to the beach twice a day and AGD enjoyed building sandcastles and paddling in the shallows. He also played golf nearby with his son, but AGD was not good at small talk and conversation was restricted to golfing matters. The move was prompted by Robin’s poor health and the same year they holidayed in St. Malo and Dinard in France. The Dennistons were a nuclear family and AGD usually partnered his daughter ‘Y’ when they played bridge, while his son Robin partnered his mother. The family played tennis in Chelsea and used public courts in Bletchley and Ashtead, Robin describing AGD as being ‘small but nippy and devious and could do spin shots which the straightforward players of those days found hard to return’. AGD and Dorothy talked endlessly about the children in the evenings. In 1938, they went to Scotland, borrowing a disused cottage half-way up Loch Striven in South Argyllshire, only a few miles from where AGD’s father had practised medicine. Their cottage could only be accessed by boat. AGD loved boats and the sea, having been brought up amongst them at Dunoon. Their party included a German, Ian Schiller, who had ‘adopted’ the Dennistons and made ‘Y’ his ‘honorary’ goddaughter. Although partially lame, he was adept on boats, which was helpful, given that all of their holiday effects needed to be transported to their holiday cottage by boat. AGD had to hurry back to London, leaving the family in Schiller’s care. In 1939, the family spent several weekends at Barton-on-Sea, having sold the bungalow in Fairfield Road. That summer they were holidaying in Fowey in Cornwall when, once again, AGD had to suddenly rush back to London.
On 1 August 1939, Sinclair had ordered the Service sections of GC&CS to take up their war stations at BP. The Diplomatic and Commercial Sections were ordered to move to BP on 15 August. At the time of the move to BP, the number of cryptanalysts had grown to around eighty-five and support staff had also increased, with staff numbers totalling around 200. In anticipation of the move, AGD wrote to all his staff on 11 July:
The War Station is to be manned from 15th August, unless otherwise ordered, in order to carry out a test mobilisation and to test war communications. Combined Navy and Air Force exercises are to take place from 15th to 21st August in which G.C.&C.S. may possibly take part.
Detailed orders for the move of the first wave will be issued later.
Leave arrangements are not to be interfered with. Heads of Sections should inform Commander Travis by 1st August which members of their sections will be on leave in order to assist the billeting and catering department.
With regard to railway fares, petrol allowances and subsistence allowances, the position should be cleared up now with the various departments concerned. It is to be hoped that similar arrangements to those of September 1938 should obtain, namely, Departments to pay full subsistence rates and the staff, being in receipt of lodging and food, should pay over two-thirds and retain one-third with a maximum of 5/- a day.
Mr. Clarke should clear up this question for Naval officers, Captain Tiltman for Military officers, Mr. Cooper for RAF officers and Commander Travis for members of the Foreign Office.1
He sent a further communication the following day:
In order to carry out communication tests the war site will be manned a.m. and p.m. 15th August by those detailed in G.C. & C. S. 1st wave who are not on leave at the time.
[Follows with instructions for those travelling by train or car.]
There will be no travelling allowances for those who do not make use of billets.
The official address for letters will be Room 47 Foreign Office and the telephone No. Whitehall 7947 but no private message is to be made from B. without authority.
The staff are warned against any conversations regarding the work with other members of the staff whilst in their billets. If occasion should arise as to what you are doing the answer should be that you are part of the aerial defence of London.
All leave was cancelled and Travis led the first wave of around seventyfour staff to BP and was in charge. He was joined by many of the Section Heads including Clarke (Naval), Miss Milne (Spanish Naval), O’Callaghan (Italian Intelligence), Craufurd (German Intelligence), Westall (Call Signs and Movements), Tiltman (Military), Jacobs (Italian), Cooper (Air) and Knox (Research). AGD himself led the second wave of around thirty-three staff a week later, along with some late arrivals. Hotels in Leighton Buzzard, Bletchley, Bedford, Buckingham and Newport Pagnell were used for accommodation, and there were separate lists for men and women.
Office space was limited at BP and AGD and his section heads were assigned rooms in the old house on the site. AGD’s office was on the ground floor in what had been the pre-war owner’s morning room. Here, he would personally welcome new staff members when they reported for work. AGD decided that it was time to strengthen the organisation by recruiting the men who had agreed the previous year to undertake secret work for the Foreign Office in the event of war. On 3 September 1939, AGD informed T.J. Wilson of the Foreign Office that they had been obliged t
o recruit men from the emergency list at the rate of pay agreed by the Treasury:
For some days now we have been obliged to recruit from our emergency list men of the Professor type who the Treasury agreed to pay at the rate of £600 a year. I attached herewith a list of these gentleman already called up together with the dates of their joining.
I will keep you informed at intervals of further recruitment.’2
The first intake arrived between 15 August and 2 September and included R. Bacon, L.W. Forster, Professor G. Waterhouse, Professor W.H. Bruford, N. de Grey, R. Gore Brown, Professor E.R. Vincent, Professor R.J.H. Jenkins and Professor T.S.R. Boase. On 7 September, AGD wrote to Wilson again with a list of the second intake, which included A.T. Hatto, Professor F. Norman, J.R.F. Jeffries, W.G. Welchman, Professor F.E. Adcock, Professor A.H. Campbell, Professor H.M. Last, A.M. Turing, F.L. Birch and Admiral H.W.W. Hope. They arrived between 4 and 6 September. Finally, L.P. Wilkinson and E.J. Passant arrived on 18 September. These twenty-one ‘men of the Professor type’ formed the vanguard of the vast expansion of GC&CS staff which would follow. Six of them had worked in Room 40, and only three, Jeffries, Turing and Welchman, were mathematicians. Six of the men were linguists, four were historians and eleven were or would become professors.